The creeping creatures were first discovered on the Thames in 1935, but it is only since the early 90s that they have started to run out of control.

There are no official statistics but the Environment Agency believes they number tens of thousands.

The Mitten or Hairy Crab is considered a delicacy in its native south-east Asia, where they fetch up to $70 a kilo and are steamed and cooked with soy sauce.

But these canny crustaceans are not as harmless as they first appear.

A delicacy back home, the crab is a menace to the Thames

Environmentalists regard them as a menace because they push out domestic breeds and burrow deep into muddy riverbanks causing them to collapse.

Steve Colclough, from the Environmental Agency, says: "This is a very aggressive animal, a very fertile animal - they breed very well. And they don't have a freshwater competitor in this country as we don't have freshwater crabs so they're occupying an ecological niche which nothing else does."

But it is not only London that is suffering the Mitten Crab infestation. According to Mr Colclough, the Rhine in Germany also has its fair share of the problem after attempts to trap huge numbers of the crabs failed.

"So perhaps it's a containment issue," Mr Colclough says.

Whatever the answer, the next time you order crab soup from the local Chinese takeaway, you could be getting something a lot less exotic than you bargained for.